The present invention relates to a method and a device for detecting signal lamps in a vehicle, in particular in a large vehicle, independently of which signal lamp type being used, filament or LED lamps, and to determine condition of said lamps, e.g. being faulty or not connected, or being connected.
Vehicle signal lamps, such as turn, brake, head and tail lights, and length or width indicator lamps, in particular those provided on a trailer to be towed by a car or a truck, require special safety measures. Accordingly, certain large vehicle regulations dictate, that it must be possible from a truck instrumentation to monitor, whether the trailer lights, especially the turn signal lamps are in working order or not. Conventionally, a trailer presence monitoring system is provided which is able to perform this task. Such a system may be a part of the electronic or electromechanical signal lamp control unit.
For the purpose of the present application the term “trailer” comprises both trailers and semi-trailers being hauled or towed by a vehicle such as a truck or tractor.
Monitoring of absence or presence of a trailer is conventionally carried out by direct or indirect measurement of the current, which is consumed by the light system of the trailer. This current flowing through the signal lamps is detected during the ON-period of the signal lamps. Since trailers generally have been provided with lamps of the conventional filament type, the current consumed by the light system of the trailer has been quite high, thus making it easy to monitor and detect the presence or absence of a trailer by measuring the current through the power line feeding the lamps on the trailer, and comparing the level of said current to a known threshold, e.g. less than 50% of nominal lamp current. With a current below this threshold, the monitoring system will indicate that the trailer lamp is faulty or not present at all. Depending on the system, the absence of one or more lamps will also indicate the absence of a trailer. In addition, because of the high currents, the measurement has been possible to perform by means of components, which have a rather poor resolution, making the components and also the measurement inexpensive.
The above mentioned current measurement principles can be performed directly or indirectly, e.g. by an electronic circuit measuring the voltage over a shunt resistor carrying the current, or by Hall effect circuits measuring the induced magnetic field around a conductor carrying the current, respectively. Alternatively, “smart power” semiconductor devices for switching on and off the current to the signal lamps can provide an electronic signal indicating the current level flowing through the device. Such “smart power” semiconductor devices comprise a low resolution A/D-converter for measuring the output current. These measurement principles work for the case where conventional filament lamps are used, and only during the ON-phase.
However, at present, it has been commercially practical for manufacturers of vehicles and trailers to use lamps equipped with Light Emitting Diodes or LED's, where the LED lights are designed as lattice networks of LED's and preloading resistors for controlling the nominal current through the LED's. Lamps based on LED technology have been utilised in particular for yellow trailer extension indicators (width and height), and turn signal lamps, but also lately as other lights as well, such as brake lights, etc.
One property of such diodes is that they consume a minimal amount of power compared to conventional lights. Diodes are advantageous in many ways, such as better service life expectancy leading to improved reliability and life cycle costs. However, it makes the monitoring and detection as explained above difficult or impossible, since the power consumption by a trailer equipped with LED-lights involves currents which will not be above the lowest resolution step of the used detector component. This may lead to the detection of an absence of a trailer, although a trailer is in fact attached properly to the vehicle. Such erroneous detection of the “absence” of a trailer will lead to a number of inconveniencies and problems for the electrical system of the vehicle, since many system parameters differs depending on the presence or absence of a trailer.
In order to overcome these inconveniencies, drivers may carry with them their own filament lamps, which they exchange with the LED lamps in case any problems occur during the monitoring process. This is time consuming, expensive and requires manual operation, which increases driving time, and thus reduces efficiency. For some trailer light arrangements, it is also impossible to exchange the lamps since the LED-lamps use non-standard sockets or no sockets at all. Another possibility would be to use “smart power” semiconductor devices with a sufficiently high resolution. Such devices may not exist, or they may be very expensive.
EP 1 473 190 to applicant discloses a device and a method for detecting the presence of a trailer provided with a subsystem of lamps of different lamp types, LED or filament, said device comprising voltage application means for applying a first voltage to power lines to said subsystem and means measuring the current consumed by components in said subsystem. Given that a LED lamp is consuming less current, a measurement is performed on the total current consumed by all lamps or the current consumed by groups of lamps. By doing this, the total current consumed by the lamps will be high enough for the detection by a “smart power” semiconductor devices with a low resolution. This detection works for the lamps during the ON-period.
Another possibility to overcome the disadvantage that a LED-lamp is not consuming a current high enough for a conventional detection systems, is to provide each LED-lamp with an additional electrical load, causing the LED-lamp to consume a current in the same order as a filament lamp. While this solution makes the monitoring system work properly, this does not allow for a detection of faulty trailer lamps. Excessive heat is also generated in the lamp arrangement.
It is desirable to provide a method and a device, which may alleviate the above problems and provide for a more accurate detection of signal lamps present for a determination of lamp characteristics, such as type and condition, which device and method are operable both for signal lamps in a vehicle and/or in a trailer.
According to an aspect of the present invention, provided are a method and a device for performing the method of detecting signal lamps in a vehicle, in particular in a heavy vehicle, being provided with a plurality of signal lamps, each being capable of switching between an OFF-phase and an ON-phase, said method comprising the steps of: during the OFF-phase of a vehicle signal lamp to be probed, inducing a probing current by connecting an electric current generator to said vehicle signal lamp circuit, the probing current being lower than the nominal current for the lamp in question; detecting the electric voltage level over the lamp circuit; and determining vehicle signal lamp characteristics such as type and condition based on said electric voltage level detection.
Accordingly, a method is provided which contrary to prior art methods utilizes voltage detection for determining type of signal lamp present and condition. Thus, simple circuitry is needed, which may be provided in a stand alone device for post installation in existing vehicles, and which does not require any alterations or supplement components to be added to the existing electric signal lamp sub system in a vehicle, such as towing truck or a trailer. Further, the present invention enables a more robust and thus accurate determination than the prior art of whether an otherwise “faulty” lamp is in fact faulty/not connected or a LED-lamp. Also, the current being supplied to a signal lamp present in the signal lamp subsystem to be probed is minimal, effectively reducing the risk of damaging any LED present.
According to an aspect of the invention, said method further comprises that the result of the determination of vehicle signal lamp characteristics is that the lamp is a LED lamp being connected when the detected voltage level is within a predetermined interval between a first level and a second level. The first level is a low voltage, preferably close to zero, and the second level is somewhat higher than the forward voltage of the diode or diodes comprised in the LED lamp. Due to the non-linear characteristics of the LED-lamp, when the detected voltage level is within such predetermined interval, the detection provides a robust and accurate determination of the lamp being a LED lamp and being connected. A LED lamp usually comprises a plurality of LED's in an array.
A signal lamp, which is either not connected or is faulty, is irrespective of lamp type effectively seen as an open circuit. A filament signal lamp which is working is effectively seen as a short circuit.
It is to be noticed, that a LED lamp, comprising one or more non-working LED's, by the present invention is not necessarily determined as being faulty. This will depend on the type of breakdown by the LED. For a LED lamp comprising several LED's, one LED may be broken but the lamp will still illuminate. If all LED's are connected in parallel, the lamp will illuminate if one LED is functioning. This means that the method will also indicate that the lamp is working, since the voltage drop will be detected as in normal.
For a LED lamp where the LED's are connected in series, and one LED is broken such that the LED is short-circuited, the lamp will be indicated as working, since the voltage drop over the lamp will lie within the predetermined interval. The remaining LED's will illuminate. If the LED is broken such that the LED is open-circuited, the lamp will be indicated as not working. The remaining LED's will not illuminate. This means that the voltage over the lamp will be the same as the voltage of the current source, indicating an open circuit, and thus a faulty lamp. The LED lamp may also comprise a combination of LED's connected in series and in parallel.
The first voltage level of the interval is preferably approximately zero or ground potential, but may alternatively be set somewhat higher, in the order of 100-300 mV or preferably lower than the voltage drop of a single LED used, depending on inherent resistances in the voltage detection circuit and current leakage. A filament lamp in working order is effectively seen as an electrical short circuit by the current generator, resulting in such a low voltage level detected.
In a further aspect of the present invention, further voltage levels may be used. This may be advantageous in order to detect the number of faulty LED's in a LED lamp with several LED's connected in series.
In a further aspect of the present invention, the probing current is in the order of 0.1 mA to 100 mA, and preferably in the order of 5-20 mA. Using such low current is safe, effective and accurate when performing the method according to the present invention. Accordingly, the service life of the components of the circuits probed is increased.
In a further aspect of the present invention the probing current is a DC current. The vehicle battery may provide such low amp DC current in a way known to the skilled person.
In one aspect, the probing current is applied over a predetermined detection time period. Thus, current generator life is extended, and voltage detection may be performed at a certain time, e.g. during start of the vehicle, or during attachment of a trailer to the vehicle. The length of said predetermined time period depends upon the number of lamp circuits to be probed or upon the effectiveness of the voltage level detection means. Alternatively, the probing current is applied between start and stop of a vehicle, or at all times, which may for example be useful during attachment of a trailer when a vehicle motor is not started yet.
The method according to an aspect of the present invention may in one aspect advantageously be used in combination with a conventional trailer presence monitoring system, in which case the vehicle comprises a trailer and wherein the method, before the step of inducing a probing current, further comprising the steps of using a conventional trailer presence monitoring system to indicate which trailer signal lamps is to be probed, and indicating to the monitoring system, which lamps are determined as being faulty/not connected and/or as being LED lamps. Accordingly, an additional measurement of trailer signal lamps is provided for a verification of, whether the signal lamps being indicated by the conventional trailer presence monitoring system as faulty are in fact faulty/not connected or LED lamps, in which case an indication, e.g. in the form of a signal, is provided to the monitoring system for indicating the faulty lamps and/or the LED lamps and/or the filament lamps, depending on type of conventional trailer presence monitoring system used. Thus, the present invention may be used in supplement to existing monitoring systems alongside the presently available prior art systems. This decreases installation and maintenance costs, and provides an accurate indication of condition and type of trailer lamps present, which is independent upon the type of trailer being attached, i.e. the signal lamps and circuits present therein. A robust method of detection is hereby provided.
For vehicles in general, and in particular for large vehicles, such as trucks or tractors, a method and system is thus provided according to the present invention to in a simple way detect whether any lamp provided in the vehicle or on a trailer being towed is a conventional filament lamp or a LED-lamp, and whether it is faulty/not connected. This is in particular advantageous for vehicles towing trailers, where the signal lamp types of the trailer are not known beforehand, i.e. the trailer is not specially adapted to being probed by existing technologies.
Preferably, the vehicle is a trailer being towed by a truck or a tractor. The vehicle comprising LED lamps being probed may also comprise other types of vehicles, not only large vehicles like trucks and trucks towing trailers, but also cars, motorcycles, busses, trains, trams, etc.
Preferably the device according to an aspect of the invention further comprises indicator means for an indication of faulty or not connected lamps to the driver of the vehicle based on said vehicle signal lamp type and condition determination. Thus, a driver may be alerted as to which faulty/not connected signal lamps are present. This indication means may e.g. be an indicator display providing one or more warning lights at to the precise location of the faulty lamps upon the vehicle, or an indicator lamp only indicating that faulty signal lamps are present, and being provided either inside the vehicle driving compartment or upon the outer side, e.g. in combination with a conventional trailer presence monitoring system.
In preferred embodiments of the device according to an aspect of the present invention, the combination of said voltage detection means and said vehicle signal lamp determination means is forming one unit, such as a voltage comparator circuit, or in combination with said current generator is forming one unit, respectively. This reduces size and number of components utilized, bringing down costs, and a voltage comparator circuit is able to perform both of the latter steps of the present method in one step. A single unit is advantageous for post-fabrication installation in any type of vehicle.